The present invention relates to a process for the recovery of TNT and RDX from Composition B-containing munitions. The munitions also contain non-explosive materials, such as a liner, a sealer, and a desensitizing agent.
Surplus munitions present a problem to the US military. Current budget constraints force the US military to prioritize its spending while effectively defending the interests of the United States. Defense budgets are further tightened because aging and surplus munitions must be guarded and stored. The US military regularly destroys a significant amount of its surplus munitions each year in order to meet its fiscal challenge. It also destroys a significant amount of munitions each year because of deterioration or obsolescence.
In the past, munitions stocks have been disposed of by open burn/open detonation (OBOD) methodsxe2x80x94the most inexpensive and technologically simple disposal methods available. Although such methods can effectively destroy munitions, they fail to meet the challenge of minimizing waste by-products in a cost effective manner. Furthermore, such methods of disposal are undesirable from an environmental point of view because they contribute to the pollution of the environment. For example, OBOD technology produces relatively high levels of undesirable NOx, acidic gases, particulates, and metal waste. Incomplete combustion products can also leach into the soil and contaminate ground water from the burning pits used for open burn methods. The surrounding soil and ground water must often be remediated after OBOD to meet environmental guidelines. Conventional incineration methods can also be used to destroy munitions, but they require a relatively large amount of fuel. They also produce a significant amount of gaseous effluent that must be treated to remove undesirable components before it can be released into the atmosphere. Thus, OBOD and incineration methods for disposing of munitions become impractical owing to increasingly stringent federal and state environmental protection regulations. Further, today""s ever stricter environmental regulations require that new munitions and weapon system designs incorporate demilitarization processing issues. Increasingly stringent EPA regulations will not allow the use of OBOD or excessive incineration techniques, therefore new technologies must be developed to meet the new guidelines.
One type of explosive system that presents a demilitarization problem are military shells that contain Composition B. Composition B is a mixture comprised of 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) powder particles as the energetic, or explosive components. Such shells also typically contain an asphalt liner material as well as other non-explosive components, such as a sealer and a desensitizing agent for the RDX particles. The most common method used to remove Composition B from a shell is the use of a steam wand to melt the Composition B from the shell. Another method is to use autoclaves that are large enough to heat the entire shell, thereby melting the energetic material, which will then flow out of an open shell casing. Such methods have the disadvantage of melting not only the Composition B, but also resulting in the removal and mixing of the asphalt liner and resin or wax-like sealer with the explosive components. The use of steam also introduces water that results in so calledxe2x80x9cpink waterxe2x80x9d (TNT contaminated water) that must also be treated before it can be released into the environment. Thus, the RDX particles will mix with the TNT, asphalt binder material and sealer. This results in a significant problem because the RDX, TNT, asphalt, and sealer are difficult to separate from each other and purify. Consequently, a significant amount of the RDX powder that becomes dispersed in the sealer and asphalt is unrecoverable.
The asphalt liner has been shown to accelerate the TNT aging process, thus leading to unstable products that could initiate spontaneous exothermic decomposition of the energetic materials. Consequently it is imperative to remove all vestiges of the asphalt liner in order to recover TNT of acceptable purity and stability. Water is also a contaminant in TNT and because it is difficult to separate it from TNT, the commercial value of any recovered TNT is reduced. A blend of such components also prevents its reuse as an explosive and significantly reduces its value in chemical conversion processes.
Another method for separating RDX from TNT is disclosed in U.S. Pat. No. 5,977,354 to Spencer, which is incorporated herein by reference. The Spencer method teaches melting out the TNT/RDX mixture and passing it through a sieve tray that collects the RDX particles contaminated with TNT. The molten TNT passes through the sieve. The collected RDX particles are then contacted with a solvent in which TNT is highly soluble. Through use of the appropriate amount of solvent, the contaminating amount of TNT is removed from the RDX particles allowing recovery of a high purity RDX component that can be re-used as a virgin energetic material. The Spencer method is primarily applicable to bulk material that did not originate from a munition casing since Spencer does not teach the separation and management of other components, such as liner and sealer material that are present in the effluent mixture of the munition cavities.
Further, Spencer does not provide for the recovery of high purity TNT since RDX is soluble in and contaminates the recovered TNT. The presence of trace quantities of RDX, asphalt liner, sealing material, as well as a wax constituent in TNT ( greater than 0.5 wt %) can adversely affect its properties and prevent its re-use in high valued applications, such as munitions. As previously mentioned, it is known that small quantities of asphalt adversely affect the impact and thermal sensitivity of TNT recovered from munitions.
While some of the above mentioned methods of recovering and separating TNT from RDX show promise for bulk material comprised of only TNT and RDX, there remains a need in the art for an effective method for separating the variety of components, including both explosive and non-explosive components that are present in Composition B-containing munitions. The present invention teaches the recovery of RDX and TNT of sufficient purity from the non-explosive components to be used in high valued applications such as munitions.
In accordance with the present invention there is provided a process for recovering the components of a munition containing explosive components and non-explosive components, wherein the explosive components are comprised of RDX in a TNT matrix and wherein the nonexplosive components are selected from a liner material comprised of asphalt and a sealer material comprised of a polymeric material and which non-explosive components are of a lower density than said explosive components, which process comprises:
a) opening said munition to expose said explosive and non-explosive components;
b) removing substantially all of said explosive components and at least a portion of said non-explosive components from the munition, which explosive components and at least a portion of non-explosive components is referred to as the feed matrix;
c) conducting the feed matrix to a first settling vessel containing water and wherein at least a portion of the non-explosive components rise to the surface of the water in said vessel and the explosive components sink at a rate to the bottom;
d) drawing-off water containing non-explosive components and passing it to a solids/liquid separation zone wherein the non-explosive solids are separated from the water,
e) recycling at least a portion of the water to settling vessel of step c) above;
f) conducting an aqueous slurry of explosive components from the bottom of said settling vessel to a solvent contacting zone wherein the aqueous explosive components slurry is admixed with an organic solvent that is substantially immiscible in water and in which TNT is soluble and in which RDX is substantially insoluble;
g) conducting an explosive components/water/solvent admixture from said contacting zone to a second settling vessel wherein a TNT/solvent solution organic phase is formed at the upper part of the vessel and an RDX solids in water phase is formed at the bottom part of said second settling vessel;
h) drawing off the TNT/solvent solution and passing it to a liquid/liquid separation zone wherein said solvent is separated from said TNT by a boiling point differential technique thereby leaving TNT in a crystallized form,
i) collecting said solvent;
j) conducting the crystallized TNT to a drying zone to remove substantially any remaining liquid therefrom; and
k) collecting the RDX solids from step g).
In a preferred embodiment of the present invention the solvent is selected from the group consisting of acetone, ethanol, methanol, and diethylether.
In another preferred embodiment of the present invention the separation technique for separating the non-dissolved RDX particles from the TNT/solvent solution is selected from the group consisting of gravity settling and filtration.
In still another preferred embodiment of the present invention, the dissolved RDX present in the solution containing dissolved TNT is crystallized by the addition of water to reduce the solubility of the dissolved RDX thereby causing precipitation and crystallization resulting in separation and settling from the liquid phase.
In still another preferred embodiment of the present invention the TNT is recovered from the solvent by evaporating the solvent and recrystallizing the TNT.
In yet another preferred embodiment of the present invention the recovered RDX particles are transferred into isopropyl alcohol for storage.
In another preferred embodiment of the present invention the solvent, after TNT separation, is condensed and recycled.
In still another preferred embodiment of the present invention the organic liner material, which remains in the shell after Composition B removal, is removed from the shell casing using a suitable second solvent, which is then flashed off, thereby leaving an organic liner concentrate.